For a long time now, Waybar has been occasionally deadlocking. The root cause is that Waybar's signal handlers, defined here:

are not async-signal-safe.

Very few standard library functions are async-signal-safe (in C and in C++). Notably, memory allocation (as used here:

The deadlock can be reproduced by toggling the bar (by sending SIGUSR1) very fast. I used this shell script:

while true; do killall -SIGUSR1 waybar; done

On my computer, this deadlocks Waybar within 15 seconds, and spamming my "toggle bar" hotkey generally reduced this to 5 seconds.

Potentially related to #348